Fuse link construction



June 15, 1937. A. e. STEINMAYER FUSE LINK CONSTRUCTION F iled May 5,1935 INVENTOR.

A TTORNEY.

.Patented June 15, 1937 FUSE LINK CONSTRUCTION Alwin G. Steinmayer,Milwaukee, Wis., assignor to Line Material Company, South Milwaukee,WisQ a corporation of Delaware Application May 3, 1935, Serial No.19,670

10 Claims.

This invention relates to improvements in fuse links.

Heretofore it has been the practice to provide in tensioned fuse links afusible section comprising a fuse wireof low melting point and lowtensile strength and also a strain wire adjacent the fuse wire and ofhigh melting point and high tensile strength for the purpose of assumingall of the tensile load and relieving the fuse wire of all of suchtensile load. As a result, the fusible section of the fuse link wascomparatively weak in torsional strength and the fuse wire would befrequently broken, if not seriously damaged, be-

fore the fuse link was placed in a fuse cartridge.

Not only s a fuse link constructed with a fuse wire and a strain wireparallel thereto inherently weak torsionally, but such links frequentlybecome so badly twisted that the fuse wire and strain wire are broughtinto intimate contact with each other, thereby changing the calibrationof the link from that which is based upon a link in which the wires areseparated from each other. Furthermore, it has been found that thecalibration of a link of this type varies with any change in distancebetween the fuse wire and strain wire even though these wires may not bein contact with each other. Even with the most careful handling, it isfound that the calibration of such fuse links varies between the timethey are manufac- 3o tured and the time they are actually placed inoperation. Therefore, it is the principal object of this invention toprovide a fuse link which has a fusible section embodying the equivalentqualities of a fuse wire and a strain wire parallel thereto and whichwill not have the defects above noted.

Restated, the principal object of this invention is to provide for atensioned fuse link, a fusible section which will retain all of thetensile strength and fusing qualities of the fuse links previouslynoted, but which will have in addition thereto greater torsionalstrength, greater flexing strength, greater heat concentration at thefusible section, and more accurate calibration for fusing purposes.

More specifically it is an object of this inven-' tion to provide fortensioned fuse links a fusible section in which the tension wire and thefuse wire are concentrically disposed, thus increasing the torsional andthe flexing strength of the fusible section, securing more accuratecalibration of the fusing qualities of the fusible section, and securinga greater concentration of heat on the fuse wire than has heretoforebeen possible.

A further object of this invention is to provide a fuse link having afusible portion terminating at one end in an enlarged cr0ss-sec-. tionalarea adapted to serve as a support for a tube of insulation surroundingthe fusible section of the fuse link thereby increasing the rapiditywith which pressure is built up in the arcing space and cause a morerapid extinction of the arc, and to provide at the other end of thefusible section an enlarged .end having a cross-sectional area less thanthe diameter of the tube and against which the pressure above referredto will exert itself to expel the free fuse section from the tube andfurther shorten the time during which an arc will exist.

Other and more limited objects will become apparent as the descriptionof this invention proceeds.

In the drawing:

' Fig. 1 is a view in side elevation of a fuse link embodying thisinvention, a portion of the tube being broken away.

Fig. 2 is an enlarged fragmentary view of the fusible portion of thefuse link shown in Fig. 1, the fusible portion being in verticalsection.

Fig. 3 is a view similar to that shown in Fig. 2, but taken at relativethereto, the fusible portion-being illustrated in dotted lines.

Fig. 4 is an enlarged sectional view taken on the line 4-4 of Fig. 1.

Fig. 5 is an enlarged sectional view taken on the line 5- -5 of Fig. 1.

Throughout the several views like parts are identified by the samereferencecharacters.

The fuse link illustrated in the drawing comprises a terminal head I, afiat substantially rigid terminal section 2, a flexible terminal section3, and a fusible section 4, connecting the fiat sub stantially rigidterminal section and the flexible terminal section.

The fusible section 4 includes a'strain wire 5' having its upper endlooped through the aperture H in the terminal section 2 and its lowerend looped through the aperture 1 in the rigid portion 8 of the flexiblesection. The ends of the strain wire are twisted about the intermediateportion of the wire after they have been passed through the apertures asindicated. This strain wire has a relatively high tensile strength and arelatively high melting point,

As clearly illustrated in Fig. 2, the strain wire is encased in ametallic sheathing 6 having a relatively low melting point and arelatively low tensile strength. I This sheathing terminates at theupper end in an enlarged knob 9 having a crosssectional area greaterthan the intermediate portion of the sheathing 6 and embedding the upperlooped and twisted end I to securely anchor the strain wire 5 relativeto the terminal section 2. The lower end of the sheathing 6 terminatesin 5 an enlarged knob II which embeds the lower looped and twisted endl2 of the strain wire 5 to securely hold the strain wire rigid relativeto the rigid end t of the flexible section 3. The knob II has across-sectional area greater than the 10 cross-sectional area of theintermediate portion of the sheathing 6, but the cross-sectional area ofthe knob I l is less than the cross-sectional area. of the knob 9 at theupper end of the sheathing. As clearly illustrated in Figs. 2, 3, and 4,the terminal section 2 is provided at its lower end with a tongue l3which is entirely embedded in the knob 9, the knob 9 being substantiallythe same in dimension as the terminal section is in width. A secondaperture I4 is shown in the terminal section 2. This aperture l4 permitsthe metal composing the knob 9 to unite at the upper end of the knob andthus give greater strength to the union between the knob and theterminal 2. As shown in Fig. 1, the terminal section 2 is provided witha notch I5. This notch is provided so that the terminal head I may bebroken off of the terminal section 2 when it is desired to adapt thefuse link to certain cartridges which will not receive the terminal headI.

In Fig. 1 a tube It surrounds the fusible portion 4 and a portion of theflexible section 3. This tube is composed of insulating material, suchas fibre, and snugly engages the knob 9 to be supported thereby. Asshown, the knob II issmaller in dimension than the inner diameter of thetube It. Thus, when the fusible portion 4 is severed the remaining lowerportion of the link within the tube may freely move to the open end ofthe tube.

The tube l6 serves a twofold purpose, namely, as a protecting elementfor the fusible portion 4 whenever the fuse link is handled prior to itsinsertion in a fuse cartridge and also as a means of building up apressure in the arcing area, tending to extinguish an arc and to forcethe severed sections of the fuse link apart more rapidly than they wouldotherwise tend to separate it the tube It were not provided.

when the fuse link is formed, the fusible por- 5 tion 4 is cast aboutthe strain wire 5 to form an intimate bond or union between the strainwire 5 and the sheathing 8 as well as between the sheathing and theterminal 2 and rigid section 8.

It has been found that this construction makes 5 a comparatively rigidfusible portion which has greater torsional strength than has heretoforebeen possible in fuses of like rating. It is found also that thisconstruction makes a fusible section, which has considerable resistance,to bending stresses, which will not change its calibrated rating beforebeing placed in operation and which will concentrate the greater portionof the heat generated by an overload upon the fusible portion andconsequently permit a much more ac- 5 curate calibration of the fusibleportion than has heretofore been possible in tensioned fuse links.

It has also been found that the cost of manuiacturing a fuse link asindicated, is less than the cost of manufacturing tensioned fuse links 7heretofore provided and also that the product is more uniformlyconsistent. It has also been found that the product can be delivered tocustomers in far better condition than has heretofore been possible withfuse links of the type noted in the statement of objects.

I claim:

1. A fuse link having spaced terminal sections each provided with atransverse aperture, a strain wire connecting said sections and havingits ends looped through said apertures and twisted upon the intermediateportion of the wire, and a fusible portion having a relatively lowmelting point and connecting the terminal sections, said fusible portionencasing all portions of the strain wire.

2. A fuse link comprising spaced terminal sections, a strain wireconnecting said sections, and a low melting encasement surrounding thestrain wire and connecting the terminal sections, the ends of theencasement being larger in cross-sectional area than the intermediateportion of the encasement and one of said ends being larger incross-sectional area than the other of said ends; in combination with atube of insulation surrounding said encasement and snugly engaging thelarger of said ends.

3. A fuse link comprising spaced terminal sections, a strain wireconnecting said sections, and a low melting encasement surrounding thestrain wire and connecting the terminal sections, the ends of theencasement being larger in crosssectional area than the intermediateportion of the encasement; in combination with a tube of insulationsurrounding said encasement 'and snugly engaging one of said ends.

4. A fuse link comprising an upper terminal section, a lower terminalsection, a strain wire connecting said sections, and a-low meltingencasement surrounding the strain wire and connecting the terminalsections, the ends of the encasement-being larger in diameter than theintermediate portion thereof and the end con-" nected with the upperterminal section being largerin diameter than the diameter of the lowerterminal section; in combination with a tube of insulation surroundingthe encasement and snugly engaging the larger end of said encasement,whereby to support the tube from the upper terminal section and topermit unobstructed movement of the smaller end of the encasement fromthe tube when the encasement and wire are severed.

5. A fuse link comprising an upper terminal section, a lower terminalsection, a strain wire connecting said sections, and a low melting fusesection connecting the terminal sections, the ends of the fuse sectionbeing larger in diameter than the intermediate portion thereof; incombination with a tube of insulation surrounding the strain wire andfuse section and snugly engaging one of said ends of the fuse section.

6. A fuse link comprising an upper terminal section, a lower terminalsection, a strain wire connecting said sections, and a low melting fusesection connecting the terminal sections, the ends of the fuse sectionbeing larger in diameter than the intermediate portion thereof and theend connected with the upper terminal section being larger in diameterthan the other end; in combination with a tube of insulation surroundingthe wire and fuse section and snugly engaging the larger of said ends."3

7. A fuse link comprising a terminal section, a flexible section, astrain wire connecting said sections, and a low melting-conductingencasement surrounding the strain wire and connecting said sections, theends of the encasement being larger in diameter than the intermediateportion thereof and the end connected with the terminal section beinglarger in diameter than the other end; in ccmbinationwith a tube ofiuula- 1 looped through said apertures and twisted about an intermediateportion of the wire, and a low melting conducting encasement surroundingthe wire and connecting said sections, the ends of the encasement beinglarger in diameter than the intermediate portion thereof and embeddingthe looped and twisted ends of said wire, the end connected with theterminal section being larger' in diameter than the other end; incombination with a tube of insulation snugly engaging the larger of saidends and surrounding said encasement and a portion of the flexiblesection.

20 9. .A fuse link comprising a terminal section having an aperture, 2.flexible section having a rigid portion provided with an aperture, astrain wire having its ends looped through said apertures and twistedabout an intermediate portion of the wire, and a low melting fusibleportion connecting said sections, the ends of the fusible portion beinglarger in cross-sectional area than the intermediate portion thereofand. embedding the looped and twisted ends of said wire.

10. A fuse link comprising a relatively rigid terminal section, aflexible terminalsection in spaced relation to the rigid terminalsection, a strain'wire electrically connecting said sections and securedin direct electrical contact therewith, and a low-melting metallicsheath embedding said strain wire and adjacent ends of said sections,whereby destructive torsional and bending stresses between said sectionsare minimized.

ALW'IN G. STEINMAYER.

